There are several types of vacuum controllers which have been used with paper making machines. Most of these controllers provide some kind of valving which connects a part of the paper making machines, such as a flat box, either to a high vacuum or to atmosphere, in order to control the vacuum supply to the paper making machine.
U.S. Pat. No. 3,766,933, issued Oct. 23, 1973, which is hereby incorporated by reference, describes a vacuum controller of the prior art. The aforementioned patent will hereafter be referred to as the Nicholson patent. The Nicholson patent shows a housing having several ports through its inner wall. There are plungers inside the housing, with a flexible diaphragm sealing between each plunger and the inner wall of the housing. In the Nicholson patent, a diaphragm performs no more than one valving function, opening or closing only one set of ports in the housing and the only way fluid can move from one chamber to another is by flowing through a port in the inner wall of the housing. This results in a complicated apparatus having several chambers. It also requires that there be a separate flexible diaphragm and plunger for each valving function to be performed. The plungers move back and forth, opening and closing ports in response to pressure changes in the chambers surrounding the plungers.
In this art, it is desirable to make the controllers as sensitive as possible to pressure changes. Any resistance to movement of the plungers reduces the sensitivity of the controller and therefore should be eliminated if possible. The Nicholson controller has a plurality of flexible diaphragms which are used for sealing and valving, and each diaphragm offers a certain resistance to movement resulting in a reduction in sensitivity of the controller.
A main object of the present invention is to provide a more sensitive controller than those available in the prior art. Another object is to simplify the design of the housing for the controller so as to reduce the cost of manufacture. Another object is to provide a design which permits a single diaphragm to serve more than one valving function, thereby reducing the number of valving-type diaphragms, which reduces the amount of resistance offered by the diaphragms. These and other objects will be obvious to one skilled in the art upon reading the description of the preferred embodiments.